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ICM May-June 2017

the length of wire that should be run to a secondary limit operating in the thermocouple circuit to maintain both safety and reliability. In 1979, when dual-seated (redundant) gas valves were mandated to be used on all central heating applications, an option was provided for connecting an ECO type device with those dual-seated valves. This would typically occur Figure 3 when a retrofit was transitioned from single-seated to dual-seated and an ECO was used with the single-seated valve as an alternative to actually installing a dualseated valve on some original equipment manufacturer (OEM) equipment. This was allowed in order to deplete existing stock of single-seated valves. It is up to the service technician as to whether he re-installs the ECO when replacing the single-seated valve with a dual-seated. Today, all water heaters have the Fusible Link type ECO. It is set to open at 195°F and is a one-time control— that means that if it opens it will not reset and the control will have to be replaced. The ECO is an additional safety that will open before the temperature and pressure relief maximums have been reached. Figure 4 demonstrates this set up. The problem with a water heater is that it is an open system. In other words, a boiler has a pressure relief valve that only opens on an increase in pressure above 30 pounds. The water heater has a T & P valve (temperature and pressure). The ECO will open and shut the system off before that pressure and temperature is reached. Once again, the charting out of readings taken will indicate what diagnostic must be followed. The Chart 2 reading of an: Open circuit 30 Closed circuit 20 If this reading was charted out on Chart 1, it would show that the power unit (magnet) was at fault. If plotted on Chart 2, it would be acceptable. One of the methods of ensuring a safety shutdown for over temperature is a Disc type ECO. Figure 5 exemplifies this method. The top illustration in Figure 5 also shows that, with the “J” Block type connection, we can obtain the closed circuit reading and, in addition, can determine 22 ICM/May/June 2017


ICM May-June 2017
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